Chlamydia pneumoniae is an etiology of acute respiratory diseases in humans. In addition, C.pneumoniae has been associated with chronic respiratory diseases and some diseases of immunopathology. The mechanisms by which C.pneumoniae infections trigger these immunopathologic diseases are largely unknown. The clinical spectrum of C.pneumoniae infection has been extended to atherosclerosis and related clinical manifestations such as coronary heart disease, the number one killer in the U.S. By multiple methods, evidence of the organism has been found in atheromas throughout the arterial tree. If the organism is shown to play a role in atherogenesis, there will be an urgent need to identify vaccine candidates and to develop rapid diagnostic methods. These measures should be aided by elucidation of those factors contributing to C.pneumoniae pathogenesis. There is a paucity of information available on virulence factors of C.pneumoniae and potential targets for prevention of infection. The proposal will seek through molecular, functional, and antigenic analyses to determine the role of following putative virulence factors by: 1) identifying and characterizing the antigens recognized by the C.pneumoniae specific monoclonal antibody because this antibody recognizes surface antigens, has infectivity neutralizing activity, and reacts specifically with C.pneumoniae; 2) identifying the C.pneumoniae antigen which elicits C.pneumoniae specific neutralizing antibodies: a 98-kDa and 42-kDa antigens containing C.pneumoniae specific reactivities recognized during human infection which are also found in circulating immune complexes in persons with coronary artery disease; 3) characterizing a novel genus chlamydial 70-kDa albumin like protein that contains neutralizing epitopes. The hypothesis of antigen mimicry will be addressed by screening sera collected from past studies on immunopathologic diseases associated with chlamydial infection. The ultimate goals of these studies are to elucidating C.pneumoniae antigens contributing to pathogenesis and immunonopathologies that will direct future studies of developing measures for prevention, intervention, and diagnosis.